Structural and Fluid Mechanical Characterization of Materials

The knowledge of the relevant structural and flow properties of a material is an important basis for the assessment whether the material is suitable for a given application. In addition, this information is a crucial part of the input data for our flow and material simulations.

Dynamic Mechanical Thermal Analysis (DMTA)

DMT-Analysis is based on the controlled application of a displace-ment or a force to a sample at a specific fixed or oscillatory rate. During the application of a force, the corresponding displace-ment is measured (or vice versa), such that the mechanical strains and stresses are determined. Examining a material sample with such a cyclic experiment for different frequencies, amplitudes and temperatures mechanically characterizes its visco-elasto-plastic behavior.

The following loading scenarios can be performed:

  • Quasi-static loading and unloading with load increase for the determination of static and plastic material behavior
  • Oscillatory and relaxation measurement of viscoelastic properties
  • Temperature sweeps for determination of temperature dependent material behavior and master curves

The availability of different load cells (25 N, 150 N and 2500 N) allows the mechanical characterization of very soft materials, e. g. nonwovens, up to very hard materials, e.g. reinforced plastic.

Cyclic Strain
© Fraunhofer ITWM
Cyclic strain (blue) and corresponding stress (red) during the test of a material.

Air Permeability Measurements

Our lab has a TEXTEST FX 3300 LABAIR IV for the accurate measurement of the air permeability of a wide range of technical textiles such as

  • nonwovens (e. g. filter media, hygiene products)
  • woven fabrics (e. g. meshes, webs)
  • knitted fabrics (e. g. spacers)

In addition to standard procedures quantifying the air permeability for a single value of differential pressure (e. g. ISO 9237), it is also possible to detect and quantify nonlinear relations between differential pressure and flow rate (e. g. as in Darcy-Forchheimer law). If the acoustic properties of a material are of interest (e. g. in the case of absorbers), the measurements can also provide the specific acoustic impedance. By combining air permeability measurements with the DMTA device, effects such as the influence of (permanent) compressions of nonwovens on their flow resistivity can be studied.

Relationship between volumetric flow rate and differential pressure
© Fraunhofer ITWM
Nonlinear relationship between volumetric flow rate and differential pressure for a filter medium.
Structural Mechanics Simulation
© Fraunhofer ITWM
Structural mechanics simulation for a nonwoven fabric with binder (yellow).

Project Examples

  • Study of the relationship between mechanical properties of composites and their components (e.g. fiber volume fraction and fiber orientation)
  • Determination of master curves for e.g. thermoplasts and rubber-like materials in terms of temperature frequency sweeps
  • Measurements of nonwoven thickness
  • Characterization of the tensile strength of nonwovens in machine direction (MD) and cross direction (CD) depending on ambient temperature
  • Permeability of filter media depending on media compression
  • Measurement of the air permeability / acoustic impedance of sound absorbers
  • Creation of digital material twins for real world materials in terms of fluid and structural mechanics for
    • different length scales (microscopic to macroscopic)
    • several simulation techniques and tools

Our Services and Competencies

  • Characterization of materials in terms of
    • grammage and thickness
    • structural mechanics: tensile, compression and bending tests incl. dependence of mechanical properties on the temperature
    • flow resistivity and acoustic impendance 
  • Online tool available for automatic creation of master curves from measurements
  • Material characterization, parameter identification, modeling and simulation from a single source 

Technical Equipment

Dynamic Mechanical Thermal Analysis (DMTA)

  • EPLEXOR 500N (Netzsch Gabo Instruments GmbH)
  • Compression, tension, 3-point-bending, immersion
  • Various measurement modes to determine dynamic and static mechanical properties (moduli and damping)
    • Arbitrary stress and strain controlled load cycles
    • Frequency and temperature sweeps
    • Relaxation and creep measurements
    • Control of air humidity
  • Determination of mastercurves
  • Maximum static load:              ±1500 N
  • Maximum dynamic load:         ±500 N
  • Maximum dynamic strain:       ±4 mm
  • Frequency range:                   0.01 Hz - 100 Hz
  • Temperature range:               -150 °C - 500 °C
DMTA testing device EXPLEXOR 500N
© Fraunhofer ITWM
DMTA testing device EXPLEXOR 500N: Dynamic mechanical thermal analysis (DMTA).
Air permeability tester FX 3300 LABAIR IV
© Fraunhofer ITWM
Air permeability tester FX 3300 LABAIR IV.

Air Permeability Measurement

  • Measurement area: 20 cm²
  • Pressure range: 20 Pa – 2500 Pa
  • Sequence mode: Measurement of air permeability for a given set of differential pressure values
  • Determination of specific acoustic impedance

Zwick Z010 Universal Testing Machine

The Z010 universal testing machine from ZwickRoell allows mechanical characterization of a wide range of materials: from foams and nonwovens to yarns, filter media, textiles, fiber-reinforced plastics and metals. Tensile, compression and flexure tests can be performed for various sample geometries. Strains and displacements can be determined with local resolution using a camera.

  • Load cells: 10 N, 100 N, 1000 N, 10000 N
  • Maximum force: 10000 N
  • VideoXtens system
Zwick Universal Testing Machine Z010
© Fraunhofer ITWM
Universal testing machine for mechanical characterization of various materials.